Compositions and process for inhibiting the polymerization of vinyl heterocyclic nitrogen compounds



tori rates here COMPOSKTEONS AND PROCESS FOR WHIBITING THEPOLYMERIZATION OF VINYL HETERQCY- CLHC NITROGEN COMPOUNDS Adriano Nenzand Giovanni B. Gechele, Milan, Italy,

assignors to Sicedison S. ..A., Milan, Italy N Drawing. Filed Dec. 30,1959, Ser. No. 862,803 Claims priority, application Italy Jan. 9, 1959 9Claims. (Cl. zen-2% By the term vinyl-pyridines there are to beunderstood monomers of the following general formula:

(CH: CH

wherein R represents the alkyl radicals (generally methyl or ethyl), andm stands for the numerals l or 2. Among the best known vinyl-pyridinesthat are commercially used, there can he cited for example the 2-, 3-,and 4- vinyl-pyridines, the S-ethyl-Z-vinyl-pyridines, the Z-methyl-5-vinyl-pyridines.

There are also known nitrogenous heterocyclic monomers, containing oneor more vinyl groups, such as for instance vinyl-quinolines,methyl-vinyl-quinolines, ethylvinyl-quinolines, variously substitutedvinyl-isoquinolines, vinyl-piperidines, N-vinyl-carbazoles,N-vinyl-pyrroliclones.

The compounds mentioned above, and particularly the vinyl-pyridines,have a marked tendency to polymerize spontaneously, much more readilythan that of other vinyl monomers, such as for instance styrene. Thereare met therefore particular difiiculties both in the storage anddistillation, and in general in all the operations wherein theseproducts are exposed to high temperatures.

There are known two types of polymers of the vinylpyridines. One ofthese is a very viscuous product, soluble in the monomer and in manyother solvents. The other one is hard, brittle, and insoluble in themonomer and in all solvents, and having a highly latticed structure; itis commonly called pop-corn and is quite often formed inside the columnsfor the distillation of the monomer; it has the particular property ofspontaneously accumulating if exposed to the presence of fresh monomer,increasing its weight, under experimental conditions, even a hundred orthousand fold. There thus arises the problem of finding some particularsubstances that will be capable of stopping the development of suchundesir able phenomena.

It is an object of the present invention to find new substances capableof inhibiting the polymerization of vinylpyridines, vinyl-quinolines andvinyl-isoquinolines.

A further object is that of finding a stabilizing agent that will beetfective in small concentrations relative to the nitrogenousheterocyclic vinyl monomer present.

Still another object is that of providing compositions containing, orconsisting of the nitrogenous heterocyclic vinyl compounds, effectivelystabilized, that may be subjected to thermic treatments even at hightemperatures,

polymerization of the vinyl-pyridines and vinyl-quino,

lines, according to the present invention, belongs to the group of thesulphonphthaleines, which are compounds of the type:

i-n Rn C I /Hln OH S 02 RH where R may be a nitric, halogen, phenolic,amine, sulphuric, or cyanide group, and n is' a numeral that may varyfrom 0 to 4 inclusive.

It has been ascertained that compounds of this class have the propertyof inhibiting the growth of both types of the above mentioned polymers;they are however particularly fitted for all operations wherein themonomer is being heated to high temperatures (distillation etc.). It isindeed known that many inhibitors called storage inhibitors, such as forinstance the para-tertiary-butylcatechol, and the phenols at large, loseremarkably their effectiveness even at a temperature not much above thenormal storage temperature.

The inhibitors according to the present invention instead maintain thesequalities even within a wide range of temperatures, and are particularlyand equally effective both as storage inhibitors, and as distillationinhibitors.

An example of a compound belonging tothe sulphonphthaleine group, havingthis property of inhibiting the polymerization of nitrogenousheterocyclic viny-l compounds is the unsubstituted sulphonphthaleine,commonly called phenol red.

In respect to the amount of inhibiting agent to be added to thevinyl-pyridines, this amount cannot be fixed a priori, since it dependson several factors, such as for instance the type of vinyl-pyridine(2-vinyl-pyridine, 4- vinyl-pyridine, Z-methyl-S-vinyl-pyridine, etc.)and the particular use required (storage or distillation).

Those skilled in this art can easily determine for every instance,experimentally, the inhibiting agent concentration-required to preventthe formation of undesirable quantities of polymer.

may vary from 0.001% up to 5%, preferably from 0.005% to 1%. Higherconcentrations (10% or more) would be operative, but often prove to beundesirable for all practical purposes.

The inhibiting agent may be added to the pure vinylpyridine as well asto the vinyl-pyridine mixed with water or other organic substances.There is well known for instance the importance of the separationprocess for the vinyl-pyridines from the alkyl-pyridines by means of'distillation; in the liquid system feeding the column there are presentwater, vinyl-pyridine, ethyl-pyridine, and other pyridic compounds, andthere is directly added to the mixture, an inhibiting agent in thesuitable rat-i0.

Although the inhibiting agent maybe mixed with the vinyl-pyridine in anyway whatever, it has been ascertained that it is preferable to establishconditions favorable to secure the maximum possible solubility. Thusforinstance it has been found that it is expedient to Patented. Nov. 28,1961.

3 introduce the inhibitor in the finest possible form, with stirring andeventually heating.

The present invention will now be further explained by examples, itbeing understood that the examples have merely an illustrative and not alimiting value, as will be understood by those skilled in this art.

EXAMPLE NO. 1

There are taken 10 gr. of Z-methyl---vinyl-pyridine carefully purified,by means of repeated crystallizations, and same is introduced into asturdy glass vial; to this is added a Weighed amount of inhibitingagent. The vial is then subjected to a freezing temperature of 40 to -50C. and repeatedly subjected to a vacuum of 1 to 2 rnms. of Hg. The vialis then sealed, taking care that the vacuum remains unaffected, andintroduced into an oil bath at 100 C. wherein the contents are keptstirred by means of a suitable apparatus, for a length of time of hours.At the end of this period the vial is rapidly cooled and its contentspoured, a drop at a into one liter of hexane, with moderate stirring.The polymer is thus slowly precipitated and then filtered through a 1-64Gooch funnel, fully leached, dried in an oven at 70 C. under vacuum, andweighed.

in the attached tables there are listed the percentages by weight ofpolymer, as obtained with diilerent inhibiting agents known or used inthe industry, and compared with that obtained with the phenol red, as anexample of sulphonphthaleine.

EXAMPLE NO. 2

The same experimental procedure described in the preceding example, wasfollowed with the inhibitors and the quantities or" same listed in Tablell where the obtained results are also shown.

Table II Concen- Inhibitor tration, Polymer grams per percentage hundredSulphur 0 2 7.6 ph 0 4 3.4 Phenol Red ulphonphthalemeL. 0 1 2.8 Phen e 02 0.8 Phenol Bed 0 4 0. 7

What we claim is:

1. A process for inhibiting the polymerization of polymerizable basicnitrogenous heterocyclic vinyl compounds having the formula selectedfrom the group consisting of;

(CHICK?) m R1-m where m is a numeral ranging from 1 to 2, and where R isa member selected from the group consisting of H and lower alkyl, saidprocess consisting in addition to said heterocyclic vinyl compounds, asa stabilizing agent, a sulphonphthaleine having the formula:

there R is a substituent selected from the group consisting of nitro,halo, hydroxyl, amino, cyano, and sulpho, and n is a numeral rangingfrom. 0 to 4, inclusive.

2. A process for inhibiting the polymerization of vinyl heterocyclicnitrogenous basic compounds according to claim 1, in which saidstabilizing agent is:

3. A process according to claim 1, wherein said stabilizing agent isadded to said basic nitrogenous heterocyclic vinyl compounds duringheating of said vinyl compounds to temperatures ranging from the meltingpoint thereof up to the boiling temperature thereof.

4. A process according to claim 1, wherein, said stabilizing agent isadded to said basic nitrogenous heterocyclic vinyl compounds attemperatures normally prevailing during storage thereof.

5. A composition consisting essentially of a normally polymerizablebasic nitrogenous heterocyclic compound having the formula selected fromthe group consisting of:

(CHZOH2) Ram-t (CH: CH2)m and (OH: 0H2)m L/ i-m Where m is a numeralranging from 1 to 2, and where R is a member selected from the groupconsisting of H 5 6 and a lower alkyl group, and as a stabilizing agentthere- 6. A composition according to claim 5 wherein said for asulphonphthalein having the structural formula: polymerizableheterocyclic compound is 2-methyl-5- OH vinyl-pyridine.

7. A composition according to claim 5 whereinsaid I 5 polymerizableheteroeyclic compound is 2-vinyl-pyn'dine. 8. A composition according toclaim 5 wherein said stabilizing agent is phenosulphonphthalein.

4 9. A composition according to claim 8 wherein said O stabilizing agentis present in an amount from 0.001% I 10 to 5% by weight. 0 RD SReferences Cited in the file of this patent 0 o UNITED STATES PATENTSwhere R is a substituent selected from the group con- 2,824,105 Smith eta1. Feb. 18, 1958 sisting of nitro, halo, hydroxyl, amino, cyano, andsulpho, 15 2,826,581 Mahan et a1. Mar. 11, 1958 and n is a numeralranging from 0 to 4, inclusive.

1. A PROCESS FOR INHIBITING THE POLYMERIZATION OF POLYMERIZABLE BASICNITROGENOUS HETEROCYCLIC VINYL COMPOUNDS HAVING THE FORMULA SELECTEDFROM THE GROUP CONSISTING OF: